One of the most frequently asked questions in the oxygen compatibility world is whether aluminum is compatible with oxygen. The answer is yes for high pressure aluminum alloy (AA) cylinders, and this is proven by the fact that several million AA cylinders are safely used around the world every day. However, some accidents have occurred with AA cylinders in oxygen service. In this paper, two main accident types are described and illustrated. The first accident occurred when devalving a cylinder which was under full pressure, resulting in a violent explosion and burning of a large part of the cylinder shoulder. The second accident occurred when a cylinder was dropped from a height of about 400 mm; again the cylinder exploded and again a large part of the cylinder shoulder burned. Tests were conducted in an attempt to understand the ignition mechanisms. In this paper, the ignition mechanisms are explained and recommendations are provided to prevent reoccurrences.